Crossed-field device



Dec. 20, 1960 INPUT FIG.I.'

ill

SE PUAN YU ET AL 2,965,797

CROSSED-FIELD DEVICE Filed June 22, 1959 OUTPUT FIG.2

INVENTORS: SE PUAN YU, BILLY D. MCNARY,

THEIR ATTORNEY.

United States atent C) ice CROSSED-FIELD DEVICE Se Puan Yu, Schenectady, N.Y., and Billy D. McNary,

Rolling Hills, Califl, assignors to General Electric Company, a corporation of New York Filed June 22, 1959, Ser. No. 821,964

13 Claims. (Cl. 315-3165) Our invention relates to microwave amplifiers and pertains more particularly to new and improved high power microwave amplifiers of the crossed-field types and particularly adapted for high-gain and high-efficiency operation.

Crossed-field microwave amplifiers, and especially magnetron amplifiers, have proved substantially attractive to radar and other high power systems designers due to certain desirable features thereof, such, for example, as ease of fabricating, inherently high efficiency, high power capabilities, wide frequency bandwidth capabilities, and satisfactory phase stability. However, heretofore, such devices have been generally characterized by low gain and it has been possible to increase gain only at the expense of etficiency with resultant undesirable power loss.

Accordingly, a primary object of our invention is to provide a new and improved crossed-field amplifier adapted for affording high gain with high efiiciency and without losses in power output.

Another object of our invention is to provide a new and improved slow wave structure for crossed-field amplifiers.

Another object of our invention is to provide a new and improved magnetron amplifier.

Another object of our invention is to provide a new and improved magnetron anode structure adapted for increasing substantially the applications of magnetron amplifiers.

Another object of our invention is to provide a new and improved device adapted for inhibiting oscillations in the vicinity of cut-off frequency and thus inherently adapted for greater stability.

Further objects and advantages of our invention will become apparent as the following description proceeds and the features of novelty which characterize our invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of our invention we provide a magnetron amplifier including a centrally disposed emitter and a plurality of resonant cavities defining a slow wave structure extending about the emitter. The

anode-to-cathode spacing increases progressively from the input region toward the output region of the device and the inter-vane spacing or sections of the anode structure decreases progressively from the input region toward the output region. Additionally, the electrical parameters per cavity are maintained constant along the length of the structure by decreasing the heights of the vanes progressively from the input region toward the output region.

tration of the vane structure of our device.

Referring now to Figures 1 and 2, there is shown a 2,965,797 Patented Dec. 20,. 1960.

microwave amplifier of the magnetron type comprising anode and cathode structures generally designated 1 and 2, respectively.

The anode structure 1 comprises a generally cylindrical conductive wall 3, the upper and lower ends of which are closed by end plates 4 and 5, respectively. Extending centrally from the inner surface of the wall 3 and longitudinally between the end plates 4 and 5 is a plurality of anode vanes 6 defining a plurality of resonant cavities which comprise a slow wave structure. The dimensions and dispositions of the vanes 6 and the particular slow wave structure formed thereby contribute substantially to the improved operation of our device and will be described in greater detail hereinafter.

The cathode structure 2 is supported centrally or co'- axially in the device by insulative support means generally designated 8 in Figure 2. The support means 8 is suitably mounted centrally in the end plate 4. The cathode 2, which is often referred to in the microwave art as a sole includes a cylindrical emissive surface 10 and, in operation of the device,.the entire cylindrical surface 10 i is rendered emissive by a contained heater (not shown).

Input and output leads ll and 12, respectively, provide for radio-frequency coupling into and out of associated input and output cavities. These leads extend through openings in the wall 3 of the device by means of metallic bushings i3 threaded into suitably tapped holes in the wall 3 and insulative seals 14 which seal the spaces between the leads 11 and 12 and the bushings 13 in a well-known manner. The leads 11 and 12 are formed at the inner ends thereof with coupling loops suitably disposed in and secured to the Wall portions of corresponding cavities and are effective for coupling radio-frequency energy into and extracting radio-frequency energy from the device. It will be clear from the following that, if desired, waveguide coupling means can be effectively substituted for the coupling means shown in the drawing.

Our device is adapted for normal operation with magnetic means (not shown), which is effective for providing a magnetic field extending longitudinally therethrough; and provided on the end plates 4 and 5 are pole pieces 15 and 16, respectively, for coaxially concentrating the magnetic field in the device. The magnetic field causes electrons emanating from the cathode to be rotated as a beam.

As clearly shown in Figure l the slow wave structure defined by the anode wall 3 and the vanes 6 extend circumferentially about the cylindrical cathode or sole 2. However, as also shown, in our improved device the space or interaction gap between the slow wave structure and the sole is smallest at the input region, or the region between the cathode and the cavity in which. the input loop is disposed, and progressively increases or tapers outwardly about the device or along the length of the slow wave structure toward the output region, or the region between the cathode and the cavity in which the output loop is disposed. Additionally, the vane-to-vane spacing decreases progressively from the input region of the device toward the output region.

By providing the close spacing between the slow wave structure and the cathode at the input region we obtain greatly increased coupling between the radio-frequency field and the rotating beam. Thus, the bunching of electrons comprising the beam and for effecting the desired energy transfer to the. slow wave structure is accomplished at a substantially lower input power or, in other words, with maximum power output and substantially higher gain.

In operation of our device and as the radio-frequency wave progresses along the slow wave structure from the input region towardthe output region the wave grows .Figure 3.

. 3 and in order to maintain high efliciency along with maximum power and higher gain all along the slow wave structure we have provided the particular electrode arrangement illustrated in the drawing wherein the interaction space or cathode-to-anode spacing progressively increases or tapers outwardly from the input region toward the output region. Thus, we obtain the maximum power and gain at each point along the slow wave structure or radio-frequency circuit without foregoing efficiency.

' Additionally, in the operation of our device the applied potential difference between the cathode and the radiofrequency circuit or slow wave structure is constant along aces-197 H V spacing effective for inhibiting oscillations in the vicinity the length of the latter. Thus, the direct current electric field intensity varies along the slow wave structure and at any given distance from the cathode. Consequently, the ratio of electric to magnetic field seen by the electrons rotationally proceeding in the interaction gap or between the cathode and slow wave structure changes progressively with the result that the drift velocity of electrons will change along the line.

In order to maintain maximum gain along the circuit, the phase velocity of the growing radio frequency wave must vary and synchronize with the changing electron drift velocity. This change in phase velocity must be accomplished without changing the synchronous bandwidth in a given frequency range. We accomplish this with our improved slow Wave structure which provides uniformity of the electrical parameters of the cavities along the full length of the slow wave structure.

Our improved slow wave structure is constructed to maintain the electrical parameters of sections of the structure constantly uniform throughout the length thereof where a section of the structure is considered to be the distance between the pair of adjacent vanes defining each cavity. By keeping the electrical constants thus uniform the frequency-impedance characteristic of the structure is maintained constant and the phase shift per section of the slow wave structure is maintained constant for any frequency in the pass band, or the guide wave length varies as the length of the section.

In order to keep the electrical parameters constant per cavity, thus to synchronize the wave and electron beam,

we adjust the capacities between adjacent vanes. This is preferably accomplished by varying the spacings between pairs of adjacent vanes and by varying the heights of the vanes which determine the intervane capacities.

Thus, and as illustrated in Figures 1 and 3, as the inter-electrode gap or anode-to-cathode spacing y increases progressively from the input region toward the output region, the inter-vane spacing d decreases progressively. Additionally, and as also seen in Figure 3, the effective heights of the vanes decrease from the input region toward the output region.

In order, however, to present vane tips of substantially uniform lengths to the beam we make our effective vane height adjustments behind the tips, as by constructing the vanes to resemble the letter H in the manner shown in With this type of vane structure the adjustment of the heights of the vanes for maintaining uniform the electrical parameters of the cavities is accomplished by varying the heights of the cross portions or bars 17 of the H-shaped vanes. Thus, and as seen in Figure 3, the heights of the cross bars 17 of the vanes 6 decrease progressively from the input region toward the output region of the device.

It will be understood from the foregoing and the drawing that the vanes need not be literally H-shaped but, alternatively, the inner ends of the vanes can resemble a horizontally extending T. It is essential only that the .horizontally extending portions be adapted for progressively varying heights or thicknesses. The vertically extending tips or segments can be of equal lengths.

Additionally, we have found the tapered line or structure including progressively increased cathode-to-anode of cut-off frequency. Thus, the device is inherently adapted for stable operation.

As also seen in Figure 1, the portion of the anode intermediate the input and output cavities which is generally designated 26 might be considered an inactive region in view of the fact that it does not propagate radio-frequency energy. 7

Thus, it will be seen from the foregoing that we have provided an improved crossed-field amplifier including an improved means for coupling the radio-frequency input and the electron beam and an improved anodercircuit adapted for providing phase velocity variation along the length of the circuit to synchronize the beam and radio-frequency wave and to control the operating point in each section of the device. In this manner we have provided an improved device adapted for increased gain and high-etficiency operation. Additionally, as pointed out above, our device is adapted by means of the tapered interelectrode spacing for greater stability.

While we have shown and described a specific embodiment of our invention We do not desire our invention to be limited to the particular form shown and described, and we intend by the appended claims to cover all modifications within the spirit and scope of our invention.

What we claim as new and desire to obtain by Letters Patent of the United States is:

1. A crossedfield device comprising an anode structure including a plurality of resonant cavities, an emitter having a portion thereof disposed directly opposite and in spaced relation to each said cavities, a signal input means and signal output means coupled to spaced regions of said anode structure, and the interelectrode spacing between said emitter and anode structure increasing progressively from the region of said input means to the region of said output means.

2. A crossed-field device comprising a cylindrical emitter, a cylindrical anode structure surrounding said emitter and including a plurality of resonant cavities extending in spaced relation toward said emitter, signal input means and signal output means coupled to circumferentially spaced regions of said anode structure, the spacing between said emitter and said cavities increasing progressively from the region of said input means to the region of said output means, and said cavities all having substantially uniform electrical parameters between said regions of said input and output means.

3. A crossed-field device comprising a cylindrical cir cumferentially emissive cathode, and a cylindrical anode structure extending about said cathode and including a plurality of vanes extending in spaced relation toward said cathode and defining a plurality of resonant cavities, wherein each cavity comprises a pair of spaced straightwalled vanes converging toward said cathode, signal input means and signal output means coupled to cavities at circumferentially spaced regions of said anode structure and the spacing between the ends of said vanes and said cathode increasing progressively from the region of the input means to the region of the output means.

4. A crossed-field device comprising an emitter, an anode structure including a plurality of vanes extending in spaced relation toward said emitter and defining a plurality of resonant cavities, signal input means and signal output means coupled to cavities at spaced regions of said anode structure, the interelectrode spacing between said vanes and said emitter increasing progressively from the region of said input means to the region of said output means, and the spacing between adjacent vanes decreasing progressively from the region of said input means to the region of said output means.

ture and the eifective areas of said vanes decreasing progressively from the region of said input means to the region of said output means.

6. A crossed-field device according to claim 5 wherein the vertical lengths of the tips of said vanes are substantially equal and the portions of said vanes outwardly disposed of said tips vary in area progressively from the region of said input means toward the region of said output means.

7. A crossed-field device comprising an emitter, an anode structure including a plurality of vanes extending toward said emitter and defining a plurality of resonant cavities, signal input means and signal output means coupled to cavities at spaced regions of said anode structure, and said vanes being substantially H-shaped with the cross portions decreasing in height progressively from the region of said input means toward the region of said output means.

8. A crossed-field device comprising a cylindrical cathode, an anode structure surrounding said cathode and including a plurality of centrally extending vanes extending toward said cathode and defining a plurality of resonant cavities, signal input means and signal output means coupled to cavities at circumferentially spaced regions of said anode structure, the spacing between the ends of said vanes and said cathode increasing progressively from the region of said input means toward the region of said output means, the spacing between adjacent vanes decreasing progressively from the region of said input means toward the region of said output means, and the effective heights of said vanes decreasing progressively from the region of said input means toward the region of said output means.

9. A crossed-field device comprising a cylindrical cathode, an anode structure surrounding said cathode and including a plurality of centrally extending vanes extending toward said cathode and defining a plurality of resonant cavities, signal input means and signal output means coupled to cavities at circumferentially spaced regions of said anode structure, the spacing between the ends of said vanes and said cathode increasing progressively from the region of said input means toward the region of said output means, the spacing between adjacent vanes decreasing progressively from the region of said input means toward the region of said output means, and said vanes being substantially H-shaped with the cross portions decreasing in height progressively from the region of said input means toward the region of said output means.

10. A crossed-field device comprising an emitter, an anode structure including a plurality of vanes extending toward said emitter and defining a plurality of resonant cavities, signal input means and signal output means coupled to cavities at spaced regions of said anode structure, said vanes having tip portions which are substantially equal in height and portions disposed outwardly of said tip portions which vary in height progressively from the region of said input means toward the region of said output means.

11. A crossed-field device comprising an emitter, an anode structure including a plurality of vanes extending toward said emitter and defining a plurality of resonant cavities, signal input means and signal output means coupled to cavities at spaced regions of said anode structure, and said vanes being substantially H-shaped with the cross portions decreasing in height and the spacing between said vanes decreasing progressively from the region of said input means toward the region of said output means.

12. A crossed-field device comprising an emissive cathode, an anode structure including a plurality of vanes extending toward said cathode and defining: a plurality of resonant cavities, signal input means and signal output means coupled to cavities at spaced regions of said anode structure, the spacing between the ends of said vanes and said cathode increasing progressively from the region of said input means toward the region of said output means, and the spacing between adjacent vanes decreasing progressively from the region of said input means toward the region of said output means, and the elfective heights of said vanes decreasing progressively from the region of said input means toward the region of said output means.

13. A crossed-field device comprising an emissive cathode, an anode structure including a plurality of vanes extending toward said cathode and defining a plurality of resonant cavities, signal input means and signal output means coupled to cavities at spaced regions of said anode structure, the spacing between the ends of said vanes and said cathode increasing progressively from the region of said input means toward the region of said output means, the spacing between adjacent vanes decreasing progressively from the region of said input means toward the region of said output means, and said vanes being substantially H-shaped with the cross portions decreasing in height progressively from the region of said input means toward the region of said output means.

References Cited in the file of this patent UNITED STATES PATENTS 2,546,870 Sayers Mar. 27, 1951 2,687,777 Warnecke et a1 Aug. 31, 1954 2,695,929 Reverdin Nov. 30, 1954 

